I'm also seeing this exact issue on the Fire TV running on Ethernet when trying to connect to a world on an iPad. Worked fine for many months before the 15 update.
If I unplug the Ethernet on the FTV to force it to Wifi I can connect ok.
Message seen is: "You must be connected to Wifi to play with your friends."
Neil Murphy
I'm also seeing this exact issue on the Fire TV running on Ethernet when trying to connect to a world on an iPad. Worked fine for many months before the 15 update.
If I unplug the Ethernet on the FTV to force it to Wifi I can connect ok.
Message seen is: "You must be connected to Wifi to play with your friends."